1. Field of the Invention
The present invention relates to a control apparatus and a method of manufacturing the inventive control apparatus, as well as to a clutch slip control apparatus as one typical application of the inventive control apparatus and a method of manufacturing the clutch slip control apparatus. More specifically, the present invention pertains to a control apparatus for outputting a plant input to make the actual state of a general plant coincide with a target state, thereby controlling the actual state of the plant. A concrete technique applied to a clutch slip control apparatus given as one aspect of such a control apparatus outputs a plant input of clutch operation to make an actual slip revolution speed coincide with a target slip revolution speed and adjusts a slip condition based on the plant input thus output.
2. Description of the Related Art
With the advance of control theories, control apparatuses of various types have been designed and manufactured. By way of example, a clutch slip control apparatus is explained herein. Known clutch slip control apparatuses include those for controlling a slip condition of a lock-up clutch of a torque converter. Such slip control apparatuses are designed to solve contradictory problems; that is, coupling inputs with outputs of a torque converter transmits vibrations of an engine directly to a transmission in a range of low engine speed, thus worsening the ride, whereas disconnecting outputs from inputs in a wide range of engine speed does not realize effective reduction of the fuel consumption rate.
Improvement has been given to these slip control apparatuses with a view to reconciling a quick response and stable control. One example of proposed improvement includes a process of calculating a current plant input from a deviation of the actual slip revolution speed from a target slip revolution speed as well as from a differential and an integral of the deviation or from a target slip revolution speed as well as from a differential and a second differential of the deviation (see JP-B-2-586). Another example includes a process of expanding these quantities in times series to derive an increase in plant input (see JP-A-64-30966). Sufficient matching of the characteristics of the control apparatus with those of a plant enables the slip quantity to be stably adjusted to and kept at a level substantially equal to or proximate to a target value, thereby realizing the high follow-up ability over the target value without lowering the stability.
These control apparatuses, however, still have a drawback; that is, insufficient control over a characteristic perturbation in a system for controlling a clutch slip condition. When there is a significant difference in properties between individual lock-up clutches or individual slip-regulating hydraulic control systems, or when the frictional characteristics of the lock-up clutch or .mu.-v characteristics of the clutch are varied from the initial designed conditions, due to deterioration of frictional members or operating oil, to damage the stability of the slip revolution speed, the conventional control apparatuses can not realize the stable, high-speed control of the slip quantity to be substantially equal to or proximate to the target value. This issue will be described concretely with the drawings of FIGS. 36 through 38.
Characteristic perturbations in a slip control system are shown as variations in gain and phase of a transfer function from a plant input to a slip revolution speed. FIG. 36 is a graph showing a difference in designed properties between individual clutches. The characteristics of clutches are varied depending upon the instability or pressing orientation of frictional members, especially in a high frequency domain. When frictional members are worn or operating oil deteriorates thermally over time, both the gain and phase characteristics lower from the initial designed conditions in medium and high frequency domains as shown in FIGS. 37A and 37B. Such deterioration may cause the frictional characteristics to have a resonance peak in a high frequency domain as illustrated in FIG. 38. Under these conditions, the frictional members may show a so-called stick-slip behavior (repeating a series of movements, i.e., contact, revolution, and separation) and thereby cause a self-oscillation of several tens hertz. This results in totally damaging the control stability of the slip revolution speed.
The problem discussed above may be ascribed to the conventional design policies of control apparatuses. The prior art control apparatuses are designed to satisfy the stability and follow-up properties of control only under a specific condition, that is, on the assumption that control characteristics of a clutch are not significantly varied. Possible improvement applicable to the control apparatus, which calculates a current plant input from a deviation of the actual slip revolution speed from a target slip revolution speed as well as from differential and second differential of the deviation, is to change the constants of control according to the characteristic perturbations of the control system. Such improvement is, however, not practical since it makes the structure of the control system undesirably complicated while not ensuring the stability of the change-over algorithm.
The issue of characteristic perturbations always exists in real systems. In order to guarantee the stability of control, known control apparatuses generally have only a slow response. Although the slow-response control stably keeps the actual slip revolution speed substantially equal to or proximate to a target slip revolution speed under a stationary driving condition, it can not block an input torque variation of an engine or enhance the efficiency of torque transmission following a transient driving condition, in which the target slip revolution speed varies.